The present invention relates to an electronic control system for a planing or sanding machine. More particularly, the invention relates to a control system using independent measurement and control of the position of each end of the planing or sanding head of the machine, so as to produce a machine capable of planing or sanding a board or panel with minimum deviation in thickness across the width of the piece.
Planing or sanding machines are widely used in a number of industries, including the furniture and construction industries. These machines can produce boards or panels of material, most typically wood, with a uniform thickness and a smooth surface, which may then be utilized directly or further processed to produce a wide variety of useful products. In many of these applications, the thickness of the resulting material must be maintained within exacting tolerances over the entire board or panel being machined.
In a fully automated or semi-automated manufacturing process, the sanding or planing thickness must be readily and quickly adjustable, so that boards and panels of various dimensions can be accommodated without interrupting the flow of production. While manually adjustable machines have been used in the past, these systems are unsuitable for high-volume applications. The height of the sanding or planing head (corresponding to the thickness of the resulting board or panel) is therefore often adjusted via an electronic system utilizing a computer, microprocessor or similar device to control an electric motor, which can then reposition the head using a system of gears and drive shafts. Instantaneous electronic control over the position of the planing or sanding head is thereby established, and in a multi-step manufacturing process can be integrated into a computer system which monitors and controls the entire process.
Unfortunately, mechanical imperfections in the drive train connecting the motor with the planing or sanding head can lead to disparities between the intended position of the sanding or planing head and its actual position. Backlash, slack, and wear in the gear system is a common cause of such problems. Because of the tolerances required in some applications, even minor inaccuracies in head positioning and board thickness are sometimes unacceptable.
In an attempt to resolve this problem, planing or sanding machine manufacturers have developed systems designed to monitor and correct the actual position of the planing or sanding head. In the typical system, an electronic linear measuring device is used to track the position of the planing or sanding head with a high degree of precision. This information is fed into a central processing unit, microprocessor, or similar electronic device, which then provides an electric motor with the instructions necessary to maintain the desired head position with respect to the item being processed.
In the systems of this type in use to date, however, a problem arises because a single control system is used to control the movement of the planing or sanding head across its entire width. Typically, the linear measuring device and motor are positioned at one end of the head, and the other end is linked to the motor via a connecting shaft and gearing arrangement. Both ends of the planing or sanding head therefore track together.
However, in actual operation this system may result in substantial disparities in thickness across the width of the board or panel being machined. These disparities are caused by natural limitations in the accuracy with which the movements prescribed by the control system on one end of the planing or sanding head are conveyed by gears and shafts to the other. The resulting inaccuracies may be substantial enough to cause unacceptable deviations in the thickness of the resulting machined product.
What is desired, then, and not found in the prior art, is a planing or sanding machine control system that will take account of these problems, and produce a precise and uniform thickness across the entire width of the board or panel being processed.
It is the primary object of the present invention to provide an electronic control system for a planing or sanding machine that is capable of maintaining a uniform thickness across the entire width of the board or panel being processed. In the improved system disclosed herein, dual and independent control of the two ends of the machine""s planing or sanding head is established. A linear measuring device and motor-driven drive unit is positioned at either end of the head, and linked via a computer, microprocessor or similar electronic device to provide separate control of the movement of each end of the head.